On Mon, Sep 16, 2024 at 4:41 AM Nikunj A. Dadhania <nikunj@xxxxxxx> wrote:
>
>
>
> On 9/13/2024 11:12 PM, Jim Mattson wrote:
> > On Wed, Jul 31, 2024 at 8:16 AM Nikunj A Dadhania <nikunj@xxxxxxx> wrote:
> >>
> >> When Secure TSC is enabled and TscInvariant (bit 8) in CPUID_8000_0007_edx
> >> is set, the kernel complains with the below firmware bug:
> >>
> >> [Firmware Bug]: TSC doesn't count with P0 frequency!
> >>
> >> Secure TSC does not need to run at P0 frequency; the TSC frequency is set
> >> by the VMM as part of the SNP_LAUNCH_START command. Skip this check when
> >> Secure TSC is enabled
> >>
> >> Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
> >> Tested-by: Peter Gonda <pgonda@xxxxxxxxxx>
> >> ---
> >> arch/x86/kernel/cpu/amd.c | 3 ++-
> >> 1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> >> index be5889bded49..87b55d2183a0 100644
> >> --- a/arch/x86/kernel/cpu/amd.c
> >> +++ b/arch/x86/kernel/cpu/amd.c
> >> @@ -370,7 +370,8 @@ static void bsp_determine_snp(struct cpuinfo_x86 *c)
> >>
> >> static void bsp_init_amd(struct cpuinfo_x86 *c)
> >> {
> >> - if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
> >> + if (cpu_has(c, X86_FEATURE_CONSTANT_TSC) &&
> >> + !cc_platform_has(CC_ATTR_GUEST_SECURE_TSC)) {
> >
> > Could we extend this to never complain in a virtual machine? i.e.
>
> Let me get more clarity on the below and your commit[1]
>
> > ...
> > - if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
> > + if (cpu_has(c, X86_FEATURE_CONSTANT_TSC) &&
> > + !cpu_has(c, X86_FEATURE_HYPERVISOR)) {
> > ...
>
> Or do this for Family 15h and above ?
I don't think there exists a virtual firmware that sets this bit on
older CPU families. In fact, before my referenced commit, it wasn't
possible.
> Regards
> Nikunj
>
> 1. https://github.com/torvalds/linux/commit/8b0e00fba934
Something like this is necessary for existing versions of Linux. I
would like to have set HW_CR.TscFreqSel[bit 24] at VCPU creation, but
Sean would not let me. So, now userspace has to do it right after VCPU
creation. I don't have any intention of adding the code to qemu, but
maybe someone will.
